Prepping for Tile: Cleaning and Flattening the Subfloor

And with that, the painting is done! At least until the cabinets go up. But before we can think about cabinets, we have to think about the floor. That’s right, it’s time to lay some tile.

WOOT!

Of course, I have no idea what I’m doing, since I’ve never laid tile before. So I started by googling around the interwebs and I found this great in-depth series over on One Project Closer about how to lay tile. I was specifically concerned about one thing:

See that gap underneath the straightedge?

This will be the highest-traffic area in the kitchen, and I was looking for the best way to even it out. We had a bunch of cracked tiles in the old kitchen, before we tore the whole thing out; I don’t want to risk having cracked tiles in the new kitchen as well. Remember when we pulled up the entire subfloor and re-leveled the joists in an attempt to level the floor? I’d hate to think that was all in vain.

So I was particularly interested in Step 4 of OPC’s tutorial, where they explain how the pros even out a floor before laying tile. Armed with this information, I headed to The Tile Shop to stock up on mortar and grout and maybe a little more info.

I got the supplies I needed, plus a few extra tips from Don at The Tile Shop. I came home ready to get down to business. Step One: clear out the kitchen.

…because you can’t tile a floor if you’re using it to store your pile of junk.

Ahhh, much better. Step 2: Clean the floor. If I were writing a tutorial on how to prep a floor for tile, here’s how it would go:

The instant the subfloor is laid down, cover it with rosin paper.

When you’re ready to tile, pull up the paper, vacuum the floor quickly just to be sure it’s clean, and start laying your tile.

That would have been the easy way to do it. Here’s how I actually did it. First I gathered my Dream Team for the unenviable task of scraping up all the joint compound and paint drippings:

A scraper, a bit of coarse sandpaper for anything the scraper couldn’t get, a screw gun (for making sure all the screws were countersunk), a shop-vac, and a bucket of clean water with a sponge or rag. Oh, and a knee pad. Because I spent a lot of time on my knees. My method was to work in one small area at a time (about 3′ x 3′). I’d start with the scraper, which got most of the joint compound chunks off really easily. Then I’d follow with the sandpaper, which was better at getting paint drips off. I’d use the screw gun to sink any screws that weren’t flush with the surface (or lower). Then I’d vacuum the area, and finally wipe it down with a damp cloth to get any remaining drywall dust.

“It’s important that the subfloor is free of dirt, debris, paint, drywall compound, etc. Jim and Rich meticulously went over the floor with a scraper and brush. If this had been a plywood or OSB subfloor, the guys would have been on the lookout for protruding screws, nails or staples too.”

I figure if this is how the pros do it, it’ll probably work for me, too. And it was definitely necessary; you can see in the picture below the difference between the top sheet of plywood (which had been cleaned) and the bottom sheet (which hadn’t been cleaned yet).

Once that was done, it was time to put some of Don’s advice to work. One of the things he told me was that I didn’t have to use self-leveling cement or any other special product to fill in the valley in my floor—regular old thinset would work. Just put down a layer, use a straightedge or a piece of lumber to screed it off, and allow it to cure before laying tile. Easy peasy. Don’s second piece of advice was to put a few nails or screws into the floor where I was going to be filling in, but let them stick out a little bit.

This would give the thinset something to grab on to. I’d never heard of this before, but then again, I only have about 8 hours of experience with this stuff. Any by “experience” I mean “googling things on the interwebs.” So, you know…I figured it couldn’t hurt. I staggered 6 nails around the deepest part of the valley, made sure none of them stuck up above the straightedge, and mixed up my mortar. Then I spread it over the floor and used my straightedge to screed it off, just like the pros did on One Project Closer.

I mixed it a little thin because I thought it would be easier to level out. In hindsight, this wasn’t necessary. For one thing, it takes longer to dry. And for another, it made it too easy to spread; I ended up with a fairly thin layer, and now I’m thinking I may have to do another coat in order to completely fill in the valley. Which means another 24 hours of dry-time before I can get to the fun part. But since the first coat isn’t dry yet, I’ll just have to wait and see.

In the mean time, today’s task is to figure out the pattern. We’re just using 12×12-inch tiles, but I want to lay them on a diagonal (because keeping things simple isn’t any fun, am I right?). I don’t want to end up with weird cuts or tiny little pieces on visible edges of the floor. And our room is kind of kind of funny-shaped, so dry-fitting is the only way I know of to make sure that doesn’t happen.

Comments

I don’t know. It probably depends on how bad the dips in your floor are. Backerboard provides rigidity and probably does a pretty good job of alleviating minor hills/valleys, but it might just conform to bigger slopes.